linux-kernel - Re: [PATCH] vfio/iommu_type1: report the IOMMU aperture info

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Message-Id: <7cf3e03e-e9b4-0e27-098b-3bc391abcf96@linux.vnet.ibm.com>
Date:   Thu, 30 Nov 2017 15:16:03 +0100
From:   Pierre Morel <pmorel@...ux.vnet.ibm.com>
To:     Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>
Cc:     "cohuck@...hat.com" <cohuck@...hat.com>,
        "borntraeger@...ibm.com" <borntraeger@...ibm.com>,
        "zyimin@...ux.vnet.ibm.com" <zyimin@...ux.vnet.ibm.com>,
        "pasic@...ux.vnet.ibm.com" <pasic@...ux.vnet.ibm.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vfio/iommu_type1: report the IOMMU aperture info

On 30/11/2017 13:57, Jean-Philippe Brucker wrote:
> Hello,
> 
> On 30/11/17 11:34, Pierre Morel wrote:
> [...]
>> +/**
>> + * vfio_get_aperture - report minimal aperture of a vfio_iommu
>> + * @iommu: the current vfio_iommu
>> + * @start: a pointer to the aperture start
>> + * @end  : a pointer to the aperture end
>> + *
>> + * This function iterate on the domains using the given vfio_iommu
>> + * and restrict the aperture to the minimal aperture common
>> + * to all domains sharing this vfio_iommu.
>> + */
>> +static void vfio_get_aperture(struct vfio_iommu *iommu, uint64_t *start,
>> +				uint64_t *end)
>> +{
>> +	struct iommu_domain_geometry geometry;
>> +	struct vfio_domain *domain;
>> +
>> +	*start = 0;
>> +	*end = U64_MAX;
> 
> I wonder if the default values should also reflect what the VFIO
> implementation actually supports. Looking at vfio_dma_do_map, a 32-bit
> host will reject any iova greater than 32 bits. In addition,
> vfio_dma_do_unmap doesn't support unmapping the last page of a 64-bit
> address space (existing IOMMUs would probably reject map requests with
> IOVA > 52 bits anyway, but if they don't report a domain aperture, VFIO
> can't guess it).
> 
> I think it's convenient to use VFIO_IOMMU_UNMAP_DMA on the full address
> space when an unmap-all is needed, maybe we could provide default aperture
> values that help doing this? (~0U for 32-bit and (~0ULL - PAGE_SIZE) for
> 64-bit)
> 
> Thanks,
> Jean
> 

Thanks, I will take care of this.

Pierre


-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany